How to calculate concrete
- Get cubic feet. Length × width × thickness, all in feet.
- Divide by 27. A cubic yard is 3 × 3 × 3 ft = 27 cu ft.
- Convert to metres. 1 cubic yard = 0.765 m³; 1 m³ = 1.31 cubic yards.
- Round up the order. Add 5–10% and round up to the plant's step.
Worked example: a 20 × 24 ft driveway, 4 inches thick
- Volume: 20 × 24 × (4 ÷ 12) = 160 cu ft. Plus 5%: 168.0 cu ft.
- Yards: 168.0 ÷ 27 = 6.22 cubic yards.
- Metres: 4.76 m³, so order 5.00 m³ from the plant.
Cubic yards to cubic metres
| Cubic yards | Cubic metres |
|---|---|
| 0.5 | 0.38 |
| 1 | 0.76 |
| 2 | 1.53 |
| 3 | 2.29 |
| 4 | 3.06 |
| 5 | 3.82 |
| 8 | 6.12 |
| 10 | 7.65 |
1 cubic yard = 0.764555 m³.
Concrete formulas by shape
All measurements in feet; divide inches by 12 first. Results are in cubic feet.
- Slab
- length × width × thickness
- Round slab
- π × (diameter ÷ 2)² × thickness
- Continuous footing
- total length × width × depth
- Pad footing
- length × width × depth × number of footings
- Monolithic slab
- length × width × thickness + perimeter band × (edge depth − thickness), where perimeter band = length × width − (length − 2 × edge width) × (width − 2 × edge width)
- Bell footing
- π × r² × pier height + π × bell height ÷ 3 × (R² + R × r + r²), with r = pier radius and R = bell radius
- Wall
- length × height × thickness
- Column / pier
- π × (diameter ÷ 2)² × height
- Post hole
- (hole area − post area) × depth; round hole π × (diameter ÷ 2)², square hole width²
- Tube / ring
- π × [(outer ÷ 2)² − (inner ÷ 2)²] × height
- Curb & gutter
- [curb depth × (curb height + flag thickness) + gutter width × flag thickness] × length
- Steps (solid, n steps)
- width × rise × run × (1 + 2 + … + n). With a landing, the landing is the top step: width × rise × [run × (1 + … + (n − 1)) + landing depth × n]
Cubic yards = cubic feet ÷ 27. Cubic metres = cubic feet ÷ 35.31.
Frequently asked questions
How do I convert yards of concrete to cubic metres?
Multiply by 0.765. Ten cubic yards is 7.65 m³; one cubic metre is 1.31 cubic yards.
How many yards of concrete do I need for a 20x20 slab?
At 4 inches thick: 4.94 cubic yards, or 5.19 with 5% extra (3.96 m³).
How much does a yard of concrete weigh?
About 1,840 kg (4,050 lb). A cubic metre weighs about 2,400 kg.
About the prices
Costs are estimated ranges with source and date, never a quote. Enter your local prices under "Use your own prices", or read how we estimate prices.